Super Efficient Exterior Insulation Details with Rockwool (For Architects + Builders)

Exterior insulation is one of the best investments you can make if you're building in a colder climate. Apart from providing thermal comfort and energy efficiency, rigid exterior insulation significantly improves the walls' durability by preventing condensation that can lead to mold and rot problems and keeping the framing closer to interior conditions. Using rigid mineral wool, such as Rockwool Comfortboard, on the exterior will also allow the wall assembly to dry to the exterior unrestricted while providing resistance against wildfires as well as deterring pests like ants and termites.
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[@ASIRIDesigns]

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[@joniboulware1436]

I saw on the build show where 3 inches of Rock Wool was applied over 3/4 advantech and the engineer indicated the furring strips only needed to fully embed in the Advantech, not the wall studs. The vertical siding was apparently not very heavy.

[@ForrestGums]

Great video! A few considerations for the viewer turned comment reader: 1. When using XPS, EPS, or polyiso. as exterior insulation instead of the mineral wool discussed in the video, it typically reduces the drying capacity of the wall assembly, particularly in climates where a vapour control layer (barrier) is required on the interior side of the assembly. So, if the wall assembly gets wet (e.g., via condensation resulting from convective moisture transport through a discontinuous air barrier), it is anticipated to dry faster when mineral wool is used as an exterior insulation versus foam board products. The longer the wood stays wet, the more likely mould growth and deterioration are to occur. 2. I'd anticipate the effective thermal resistance of this assembly to be somewhere closer to R-35 rather than the R-21.5 shown. I believe a 45% reduction in thermal resistance (nominal to effective) for a wood-framed, exterior insulated assembly is a little high. ASIRI Designs, small math error or am I mistaken here? 3. Where possible, it is generally a best practice to shingle lap your membranes, such as over the base-of-wall flashing shown. The theory here is that if in 5, 15, 25 years the adhesive on the flashing tape begins to fail, then the shingle lap of the membrane will at least direct bulk water out of your assembly as opposed to into it. This is fairly inconsequential with this detail, with a continjuous membrane behind the flashing, but may be more important at window head details, or through-wall flashing details. This obvoiusly doens't apply if the liquid-applied flashing and sheathing membrane discussed here is used, as it is anticiped they'd bond and form a seamless transition. I love the content, ASIRI Designs. You're producing the best building enclosure detailing information that I've found on KZbin and are a great resource - thank you!

[@ASIRIDesigns]

Thank you so much for your comment, all of your points are 100% spot on! With regard to the effective thermal resistance, there are several ways you can calculate it. Some people include fenestration in the calculation for total wall R-value, others calculate it as a percentage of the framing in terms of surface area which can be anywhere from 15-20% of the building, and deduct that percentage from the nominal R-value of the assembly, or you can base the calculation off of the worst performing component(s) in the wall assembly.

[@XYZ-Drafting_and_Designs]

Love the channel. In depth information. Thanks

[@gogomogo3632]

Amazing, great video. Thank you

[@eliinthewolverinestate6729]

We use mineral wool batts with mineral wool board over it on masonry walls, and then low perm barrier, with air gap, and masonry veneer. We use wall ties for veneer to help hold insulation too. Great video as always.

[@ssmith2019]

Good video, BUT please show a wall assembly for stucco exterior since that is the predominant exterior application in the southwest mountainous (cold) regions ?

[@machickman4041]

Great video!! Would love to see the detail for slab on grade.

[@greaterbw]

I’m about to build and Rockwool is definitely what I’m going with and using standard Zip sheathing but I will pay close attention to sealing the slab to the wall and I’ve decided there’s no way I’m using tape I’m going fluid applied I think the tape is just a future failure point in 10-20 years. I’m just looking into cheaper alternatives to the Zip fluid.

[@ASIRIDesigns]

Most STPE (silyl terminated polyether)-based flashing products will work as a substitute for the ZIP liquid flash, like Prosoco's FastFash - though you may want to reconsider using the liquid flash product from ZIP since it would all be covered under the same warranty.

[@bobbray9666]

Zip-R is the most practical exterior insulation for proper water tight installations. No window bucks to build, no furring strips, no WRB install and better water/air tightness without a big learning curve by using Zip tape/liquid flashing to seal it all up. It also has higher R-values per thickness, so Zip-R12 can be nailed to 2x4 framing and normal window jambs for 2x6 framing fits perfectly. Just need to follow the prescribed nailing patterns. The labor savings are much less too using Zip. Wall drying concern is eliminated by stopping vapor at the sheathing surface and adding a plastic mesh rainscreen behind the siding for drainage/ventilation.

[@ASIRIDesigns]

There are pros and cons to every system, I definitely like ZIP-R and applaud Huber for their innovation, and have recently specified it on my last project to simplify installation for the contractors. It's not a silver bullet though and I would caution those using it in colder climates since you're limited to R-12 exterior insulation, not to mention you really need to coordinate the use of the sheathing with the structural engineer since they may need to add additional shear walls or hold downs.

[@CMCraftsman]

Yes, in RI on the coast, Zip R didn’t meet the shear requirements in that wind zone so you had to sheath the house with CDX then sheath over that with Zip R if you wanted to use it. I’m now in VT and Zip R is quite popular here.

[@bobbray9666]

@@ASIRIDesigns R-12 is more than adequate here in zone 6A for exterior insulation. Our walls have closed cell foam in 2x4 studs for a total wall R-30. Windows are getting much bigger in new homes where a good deal of energy is lost or gained, even with triple pane which are a little over R-5 or about 60% less than R-12 ext insul. You can do better than R-5 triple pane but it gets $$$$. Most use double pane around here and spend the savings on more efficient HVAC.

[@xokissmekatexo]

@asiridesigns Fantastic video! I am in the “planning” phase of new construction and wondering if I should do this. I am located in Provo Utah, it feels cold to me in the winter, hot in the summer. I talked with a few builders and they don’t think external insulation is needed but then I don’t see a lot of high performance homes out here either. You quick circled zones 1-3 on your diagram when mentioning “cold” so maybe I don’t need external insulation? I think I am zone 5. Thoughts?

[@LuminairPrime]

Thank you for pointing out the loss of insulative value due to wood framing touching the exterior wall. Do you think there is a big "bang for the buck" to be gained by using a sheathing that has rigid foam pre-attached on the back side for thermal decoupling?

[@user-kr1pq3ix1c]

What about extending the outboard layers of rigid insulation below-grade to have continuous insulation throughout an occupied basement as well?

[@1Akanan1]

I will soon change my sidings for james hardie board. Currently have cedar planks. Because we aren't changing the windows. I'm somewhat limited on how far off the wall i can add insulation. My house is 1981, 2x6 walls with fiberglass batt and (super thin) vapour barrier inside. I want to add 1 inch XPS on exterior wall. WRB, 1 inch XPS, furring strip, hardie board. I'm zone 4 (Vancouver Island). Since i watched your video i'm suddenly unsure it's a good idea, I don't want to cause condensation pockets. The main reason to add it it's to have a continous airbarrier, the vapour barrier in the house is butchered around every opening like elect. Box, door and windows.

[@coasttal123]

I recently saw a video where a couple had built their own home. They did a couple inches of closed cell, then added batts. They found the batts later to be soaked with water (condensation). They happened to be in the upper midwest. The problem was the hard surface of the closed cell gave a surface for condensation each time that surface dropped below the dewpoint. However, if the entire wall had closed cell from sheathing to drywall, they would not have had the condensation as the interior surface would have been too warm and the outer surface was too cold. Moisture will not occur inside of a homogenous material and will only occur on its surfaces.

[@ASIRIDesigns]

That's exactly right, and it comes back to the need to use the right ratios of insulation to prevent condensation. The same ratios apply to closed cell foam as rigid insulation, however, I suspect there was substantial air leakage in those walls depositing moisture onto those cold surfaces. Closed cell spray foam is tricky to work with because it can crack especially in cold climates due to expansion and contraction of the framing components. If that spray foam cracks, you've immediately violated the integrity of the air barrier, allowing warm moist air from the interior to pass through those cracks and condense. I'm now in the camp of avoiding spray foam wherever possible and opting for either rigid insulation instead or a smart vapor retarder membrane.

[@CMCraftsman]

Yes, the problem most likely wasn’t the insulation choice but more the care involved in the installation and preservation of a vapor retarder through drywall stage and the neglect to install or run an ERV or HRV in the home.

[@rangerdoc1029]

Or if they hadn't added the rock wool

[@rangerdoc1029]

​@@CMCraftsmanwasn't an HRV or Erv problem, the house was never even occupied

[@coasttal123]

@@ASIRIDesigns I think the moisture came from the inside, and not from the outside. I am not a fan of flash and batt.

[@BittyVids]

My house has plastic sheeting in the walls as a vapor barrier. I plan to insulate the exterior when I replace the siding in a couple of years. Since that plastic is perm 0, would I be able to insulate with eps or xps or would I need something more permeable like comfort board? If I understand correctly, I can’t use foil faced because like the plastic sheeting, it’s also perm0 and will trap moisture in my walls? I’m in zone 3 New England.

[@brianwball40]

I don't think your effective R value is correct at 4:20. Should be more like 31. Wood framing members reduce the R value of the wall cavity insulation (by roughly 30%), but the exterior insulation should be at almost 100% effectiveness. Why add R16, if you only get an additional R6?

[@lrw-86]

At 2:04 you mention creating a drainage gap when using rigid foam exterior insulation. Typar drainable peel and stick, or a drainage mesh are two examples. If you choose these products, what would make the most sense for an air barrier?

[@coasttal123]

Would you reference the study's that have determined the thickness of the rain screen. I keep hearing 1/16", 1/8", 1/4" etc. and see folks using 3/4" batten. I would really like to see the study that has determined the recommended width.

[@danwright5329]

Is it necessary to use the hydrogap sa verses the non sa hydrogap?

[@ivan.bucher]

Do the steel screws puncture the vapor barrier?

[@ivan.bucher]

Do you have ICF assembly details available?

[@rkf053fitz]

If one were applying exterior insulation (mineral wool) over the main floor walls and a heated crawlspace on an existing house in a cold climate, what would be a good treatment for the bottom of the insulation? The same bug screen or would there be a better method for both keeping bugs out and as a capillary break?

[@ASIRIDesigns]

Great question. The above grade walls would get the same treatment with a bugscreen at the bottom, and any rigid mineral wool located below grade will need to be protected with some sort of protection course/protection board, and drained with a dimple mat. The dimple mat can also double as the protection course. The top of the rigid insulation located below grade would need to be protected as well, I like to use either coil stock or metal flashings.

[@jimclose7485]

You show a gap between exterior side of sheathing and exterior rock wool. That gap is filled with cold air, correct? If so, does that exterior rock wool provide any insulative effect? What am I missing?

[@mahdiokasha6265]

Is the air barrier in this case also a vapor barrier?

[@MurDocInc]

Exterior insulation is expensive and complex, double stud or stagger stud with cellulose is much cheaper and closer to tradition building.

[@ASIRIDesigns]

I like double walls and they do tend to be slightly cheaper, however, you still have to contend with vapor condensing on the backside of the sheathing in cold climates and the other complexities around keeping water away from those walls. Air tightness is absolutely critical in these double wall assemblies, and either require the use of a taped smart vapor retarder on the interior side or taped sheathing located on the interior side of the exterior wall to provide an air barrier and to throttle vapor flow outwards. There are a couple of papers from Kohta Ueno from Building Science Corporation on double walls. Perhaps this will be a good topic for a future video.

[@joniboulware1436]

It seems like there would be risk of missing the studs with those very long screws.

[@MurDocInc]

@@joniboulware1436 yep, usually builders use 3/4 sheathing when dealing with thick exterior insulation. So if they miss the stud, there's still some bite in 3/4 sheathing. They also can't remove the screws cause that would be a leak in air barrier.